The field of the invention is concurrent hydrogen and carbon dioxide production.
Complex mixtures of gases such as refinery gases or offgases from combustion processes are frequently employed as starting materials in the production of purified gases, and various systems have been developed to concurrently isolate at least 2 or more gases at a relatively high purity (i.e., greater than 90% (v/v) from a single gas mixture.
Some systems employ a serial configuration of PSA units, wherein a first PSA unit has a different selectivity from a second PSA unit, and wherein the offgas from the first unit is directed to the feed end of the second PSA unit. An example for this configuration is described by R. Kumar in U.S. Pat. No. 4,913,709. Kumar""s serial configuration of PSA units with beds having non-identical adsorption specificity is favorable in cases where relatively high volumes of offgas are to be purified 1 at a time. However, the complexity and number of coordinated cycle steps generally increases due to the different physico-chemical properties of the adsorbent beds, thereby adversely increasing cost and maintenance requirements.
Other systems utilize configurations with a PSA unit and a non-PSA unit as for example described in U.S. Pat. No. 4,553,981 to Fuderer. In Fuderer""s system, carbon dioxide is removed as a waste gas from a feed gas stream by a CO2 scrubber, and the CO2-depleted stream is subsequently fed into a H2-PSA unit. The H2-PSA offgas is then vented via a waste line into the atmosphere, or recycled to a converter or shift unit. While concurrently separating H2 and CO2 from the feed gas, Fuderer""s configuration advantageously may be employed to reduce undesirable build-up of nitrogen and/or argon in the waste gases from the scrubber and H2-PSA unit by recycling the waste gases to the reformer of shift converter. However, considerable amounts of carbon dioxide and hydrogen remain in the recycling circuit and are typically vented or combusted, rendering them no more amenable to recovery.
Still other systems employ selective membranes to separate a desirable gaseous component from the offgas of a PSA unit. For example, G. Intille describes in U.S. Pat. No. 4,229,188 the use of hydrogen permeable membranes to recover H2 from the offgas of a PSA unit. Intille""s membranes advantageously remove H2 with high selectivity in a single process step, however, the use of such membranes generally requires relatively high pressure, thereby increasing the overall energy demand. To avoid at least some of the problems associated with hydrogen-permeable membranes, Anand et al. teach in U.S. Pat. No. 5,435,836 the use of an adsorbent membrane. Adsorbent membranes typically allow hydrogen recovery at comparably low pressure with relatively high specificity. The advantage of relatively low pressure, however, tends to be offset by the need of membrane exchange, thereby either increasing the complexity of the hydrogen. plant, or necessitating discontinuous operation.
Thus, although various systems for concurrent production of desirable gases from gas mixtures are known in the art, all or almost all of them suffer from one or more than one disadvantage. Therefore, there is a need to provide improved methods and apparatus for concurrent production of desirable gases from gas mixtures.
The present invention is directed to a gas production plant comprising a gas source, a first and second separator, and a liquefying unit. The first separator receives feed gas from the gas source and produces a first offgas stream and a first product stream, whereas the second separator receives the first offgas stream to produce a second offgas stream and a second product stream. The liquefaction unit receives the first product stream and the second offgas stream thereby producing a liquefied third product stream and a third offgas stream, and at least part of the third offgas stream is combined with the first offgas stream.
In one aspect of the inventive subject matter, the gas source provides a feed gas predominantly comprising hydrogen and carbon dioxide, which is produced from natural gas via a steam reformer process. While the first separator preferably comprises a CO2 scrubber, the second separator comprises a hydrogen pressure swing adsorption (PSA) unit, and the liquefaction unit comprises in a particularly preferred aspect an autorefrigeration unit.
In another aspect of the inventive subject matter, a method of removing a first gaseous component and a second gaseous component from a feed gas employs a PSA unit that produces a first product stream predominantly comprising the second gaseous component, and a first offgas stream predominantly comprising the first gaseous component and the second gaseous component. At least part of the offgas stream is fed into a liquefaction unit that produces a second product stream and a second offgas stream, and at least part of the second offgas stream is recycled into the PSA unit.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawing. dr
FIG. 1 is a schematic of a gas production plant according to the inventive subject matter.
FIG. 2 is a flow diagram depicting a method of increasing recovery of a gaseous component from a feed gas according to the inventive subject matter.